A spark plug includes an outer shell and an insulator core assembly. A wire from a distributor or an electronic ignition system is attached at a first end of the spark plug. The second end of the spark plug projects into the combustion chamber of an engine when the spark plug is installed in the engine. The second end includes an insulator core nose from which a firing electrode protrudes. The firing electrode defines a spark gap with an adjacent ground electrode that protrudes from the outer shell.
In operation, the spark plug produces a spark in the spark gap. The insulator core nose and spark gap may become fouled by carbon buildup. This has the potential to cause a short between the two electrodes, which would prevent proper operation of the spark plug.
Carbon buildup may occur, for example, if the engine in which the spark plug is installed is run repeatedly for short periods of time without allowing the engine to heat up to a sufficient temperature to burn off carbon that builds up on the spark plug before the engine heats up. These conditions may occur during the production of an automobile, prior to delivery to the dealer. After the automobile is taken from the assembly line, the engine is started and the automobile is moved numerous times. Typically, the automobile is moved only a few feet and the engine is run only for a minute or less. The short time and distance does not provide sufficient running time to warm up the engine and burn off the carbon deposits. The engine may be run twenty times for very short periods during the automobile's production--potentially causing carbon buildup.
One solution to the problem of carbon buildup is to apply a temporary coating of silicone to the core nose to prevent the carbon from adhering to the core nose. The silicone coating burns off and exits the engine in the engine's exhaust gases after use at a normal operating temperature in which the core nose temperature rises to at least 700.degree. F. This silicone in the exhaust gases may cause damage to oxygen sensors that are used to monitor emission levels.